Add dependency management for missing Netty module

Commit 7d70b1b7 removed dependency management for native-epoll. The
netty bom only provides dependency management for the classified
module.

This commit reintroduces dependency management for it until Netty
properly provides dependency management for it [1]

[1] https://github.com/netty/netty/issues/6852

Closes gh-9501

spring-boot-dependencies/pom.xml

@@ -836,6 +836,11 @@
 				<scope>import</scope>
 				<type>pom</type>
 			</dependency>
+			<dependency>
+				<groupId>io.netty</groupId>
+				<artifactId>netty-transport-native-epoll</artifactId>
+				<version>${netty.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>io.netty</groupId>
 				<artifactId>netty-transport-native-unix-common</artifactId>